This invention relates generally to starter motors and, more particularly, is directed to an extended life starter motor for automotive vehicles.
Normal operation of automotive vehicles results in activation of the starter motor between two and four times each day. Assuming that a starter motor is activated three times each day for 350 days each year, and with an average lifetime of an original equipment starter motor being 7,500 starts, then an original equipment starter motor can expect to last for slightly greater than seven years before breaking down.
On the other hand, with high fleet start operations, such as the United Parcel Service, a starter motor may be activated approximately 135 times per day for five days per week. Based on the foregoing average lifetime of a starter motor being approximately 7,500 starts, it will be readily recognized that the starter motors used in high start fleet operations will on the average break down every two to three months. It is therefore desirable to provide an extended life starter motor for such high start fleet operations.
In a starter motor, the armature shaft is generally secured only at its ends within the starter motor housing, with the armature and commutator being positioned on the armature shaft toward the rear or commutator end thereof. Because the armature shaft is only secured at its ends, with the weight thereof being supported between the ends, there tends to be a flexing or bending of the shaft during rotation of the latter. Because of such flexing, the bushings in which the front and rear ends of the armature shaft are mounted within the housing quickly become worn. This is particularly true of the front bushing at the pinion end because the weight of the armature and commutator on the shaft is disposed toward the rear end thereof, whereby flexing is greater at the front portion of the armature shaft. As a result, the front bushing is one of the first elements to fail in a starter motor. In other words, the tolerance of the bushing becomes too wide or large, so that the drive for the starter motor may jam, causing the nose of the starter motor to tear, the shaft to break, failure of the ring gear or a combination of the above and other part failures of the starter motor.
It has therefore been proposed to utilize a center support secured to the housing and mounted on the armature shaft in front of the armature. The center support has been designed in certain applications to prevent flexing of the armature shaft. However, the center support is mounted on the armature shaft by means of a bushing. Because there is still some flexing of the armature shaft, the bushing which mounts the center support also becomes worn over time, whereby flexing of the armature shaft is not prevented after a period of time.
Another point of failure in starter motors is the solenoid-fork arrangement which biases the drive portion of the starter motor forward such that the pinion thereof engages with the engine flywheel to start the engine. More particularly, after a large number of starts, the fork tends to break, thereby rendering the starter motor useless.
U.S. Pat. No. 4,366,385 describes a starter motor of the inertia drive type which eliminates the solenoid-fork arrangement. Inertia style drives are well-known in the art, for example, as shown in U.S. Pat. No. 4,395,923. See also U.S. Pat. No. 2,204,573 for a starter motor having an inertia style drive.
With starter motors, it is desirable that the meshing of the pinion gear with the engine flywheel be as smooth as possible. It is therefore desirable that suitable lubrication be provided thereat for insuring such meshing engagement.
To effect lubrication therebetween, conventional front bushings have been provided with oil impregnated fibers. However, after an extended period of usage of the starter motor, particularly in high start fleet operations, the fiber tends to become depleted of oil. Conventional original equipment starter motors do not provide any means for relubricating the drive portion of the starter motor. An absence of sufficient lubrication may cause damage to and failure of the starter motor. It is therefore desirable that some means be provided for providing periodic lubrication of the starter motor.
Related to the latter aspect, it is to be appreciated that the starter motor housing is open at the drive end thereof to permit the pinion gear to engage the engine flywheel so as to start the internal combustion engine. As a result, engine dust, sand and the like may enter the starter motor housing at the drive end thereof. Such dust, sand and the like entering the housing interferes with the starter drive and causes failure of the starter motor. This, of course, is another source of failure of conventional original equipment starter motors.
Lastly, with conventional original equipment starters, four series connected coils are used for causing rotation of the armature shaft. The four coils, however, result in the armature shaft spinning at a speed greater than that necessary, for an inertia style drive, to spin the starter drive forward such that the pinion engages the engine flywheel. A problem with such arrangement is that the starter drive tends to impact against the forward part of the housing with a relatively large force, resulting in failure of the starter motor therefrom over a period of time. The four coils are provided in order to provide the necessary torque for starting the engine. It is therefore desirable to provide an arrangement of coils in which the engine torque is maintained, while also reducing the speed of the armature shaft.
U.S. Pat. Nos. 2,923,830 and 3,030,518 disclose a starter motor for the solenoid-fork arrangement in which three series coils are used along with a shunt or holding coil. The provision of the shunt or holding coil in such patents, however, is to hold the plunger in the opening against the frame to keep the starter engaged during normal operating load or speed of the armature, which would otherwise not occur merely with the series coils, which may have their current reduced when the engine has commenced running. A coil arrangement which utilizes three series coils and a shunt coil is also sold by Ace Electric Company of Columbus, Kansas.